Method for mixing gases with liquids

ABSTRACT

An apparatus for mixing gas with liquid comprising: 
     (a) an inner cylindrical member comprising an elongated tube having upper and lower ends and a plurality of turbines, which are free to rotate about their longitudinal axis, mounted within the tube, the turbines being spaced apart from one and another and so constructed that adjacent turbines have different rotational direction or velocity; 
     (b) optionally, an outer cylindrical member comprising an elongated tube having upper and lower ends and a plurality of openings in the lower half of the tube wall; 
     (c) a base member to which the lower ends of the outer and inner cylindrical members are attached so that the lower ends are sealed, the outer and inner cylindrical members being arranged in a concentric manner; and 
     (d) a gas inlet pipe for introducing gas bubbles into the apparatus. 
     The apparatus is useful for aerating sludge, separating the fine particles contained in a slurry, and separating particles having smooth surfaces from particles having jagged surfaces. Problems regarding plugging and tangling of the turbines with foreign materials are eliminated.

This application is a divisional application of Ser. No. 018,054, filedMar. 6, 1979, now U.S. Pat. No. 4,272,461.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of this invention generally relates to the mixing of gaseswith liquids. More specifically, it relates to the aeration of liquidsby the passage of gas bubbles through an apparatus which is verticallysubmerged in the liquid and within which apparatus the rising gasbubbles are broken up by mechanical action into a multitude of muchsmaller gas bubbles which are dispersed within the liquid.

2. Description of the Prior Art

Aeration of liquids is commonly performed, for example, to acceleratebacteriological decomposition of liquid waste, to prevent algaeformation on the surfaces of stagnant pools or ponds, and so forth. Theterm "aeration" as employed herein is to be understood as denoting theintroduction of any type of gas into any type of liquid.

The simplest method of aeration comprises introducing a gas into aliquid through holes in an appropriate supply line. Some of this gas isabsorbed as the gas bubbles rise through the liquid. Unabsorbed gasescapes from the surface of the liquid, and may or may not be capturedfor recirculation.

In spite of its simplicity, this method is very inefficient. The gasbubbles, even if small, when introduced into the liquid, tend toaggregate into large bubbles or slugs of gas as they rise. These gasslugs have comparatively small surface-area-to-volume ratios, thusrelatively little gas-to-liquid contact. This results in relatively lowrates of gas absorption by the liquid at the liquid-gas interfaces. Ifthe openings in the gas outlet are made very small to introduce smallgas bubbles, fouling or plugging of the openings often occurs. Inaddition, the transit time of the gas through the liquid may be quiteshort if the liquid container, for example, a pond or holding tank, isshallow. This short gas-to-liquid contact time further results in aninefficient rate of gas absorption by the liquid. In addition, minimumturbulence is created for disrupting the liquid-gas interfaces,disruption and renewal of the interfaces being essential for high ratesof gas absorption or mass transfer.

Some slight improvement in absorption efficiency is obtained by the useof nozzles at the gas injection openings which introduce the gas intoliquid in a swirling manner so as to create some degree of turbulence.This tends to delay somewhat the formation of large gas slugs and todisperse the gas bubbles through a large volume of liquid. However, highabsorption efficiencies are still not obtained.

More commonly used processes employ the pneumatic (or air) lift pumpprinciple. When a gas is bubbled up through an elongated tube which isvertically submerged in a liquid, the buoyancy force of the rising gasbubbles causes an upward lifting or flow of the liquid through the tube.This upward flow causes a circulation within the entire body of liquid,with the liquid being continually drawing into the bottom of the tubeand being discharged from the top thereof. Turbulence in the liquidabove the top of the tube (which is normally submerged well below thesurface of the liquid) tends to improve the absorption rate of the gasby breaking up, to some extent, large gas slugs and by disrupting andrenewing the liquid-gas interfaces (see for example U.S. Pat. No.3,032,496). The liquid circulation and turbulence caused by suchpneumatic lifts may also be used to prevent formation of ice on thesurface of the liquid, or to reduce the magnitude of surface waves, forexample in a harbor area. The absorption efficiency obtained is stillmuch less than desired, however, because large gas slugs tend to formand remain unbroken, and because the gas-liquid contact time is notappreciably increased. Therefore, a considerable amount of gas must bepumped through such pneumatic lift tubes in order that a small amountmay be absorbed by the liquid. Because of the inefficiency in theabsorption process, much of the energy used to pump the gas is wasted.

Helical tube dividers installed in some pneumatic lift tubes (forexample, U.S. Pat. Nos. 1,144,342 and 3,452,966) increase the gas-liquidcontact time by providing increased path links for the gas bubbles totravel as they spiral up through the tubes. In addition, the gas andliquid exit from the tops of the tubes with a rotational motion, therebysomewhat increasing the turbulence thereabove. However, large slugs ofgas still tend to form within the tubes, with still relatively poorabsorption efficiency. Some helical tube dividers (for example U.S. Pat.No. 1,144,342) are provided with holes interconnecting the adjacentchambers to help prevent formation of large gas slugs. There is still atendency to produce small gas bubbles and the gas absorption efficiencyis still much less than desired. Gas which is not absorbed in the bubbletransit through the liquid is either lost or must be repumped throughthe liquid. This requires additional gas pumping capacity and horsepower.

Because of inefficiencies of present pneumatic lift tube aerators, ithas been necessary to pump relatively large amounts of gas through theliquid--only a relatively small portion actually being absorbed by theliquid--and to employ a relatively large number of pneumatic lift tubes,particularly when the liquid is contained in shallow tanks or ponds andshort tubes must be used. Thus, there has been considerable wastage ofgas pumping power with resulting high costs involved in such complexaerator systems.

Some aerators include a motor-driven, horizontally rotating submergedturbine. The non-enclosed turbine is generally positioned above a sourceof gas bubbles and is used to break up and disperse the released gasbubbles and to create turbulence in the liquid. Other aerators employmotor driven, vertically rotating, non-enclosed turbines or paddles at,or just below, the surface of a liquid. Such aerators usually rely uponthe air above the surface of the liquid, some of which becomes entrappedin the churning liquid, for aeration. However, motor-driven aerationsystems are expensive to produce, to operate, as well as to maintain. Asource of power for the motor must also be available.

Most recently, an aerator having high efficiency for dispersing the gasin the liquid is set forth in U.S. Pat. No. 3,969,446. The aeratorcomprises an elongated tube having openings at both ends and havingmounted therein one or more turbines which are free to rotate about thelongitudinal axis thereof. The tube is vertically submerged in a liquid,for example, in a lake or pond of water. Air or another gas is suppliedto the lower end of the tube. Gas bubbles rising through the tube causean upward flow of liquid therethrough. The turbines are rotated solelyby this upward flow of gas and liquid. This rotation of the turbinecauses the gas bubbles to be broken up into a vast number of muchsmaller gas bubbles which are dispersed throughout the liquid so thatoptimum gas absorption may occur. When more than one turbine is used,the turbines are so constructed that adjacent turbines rotate either atdifferent speeds or in counter-direction to thus optimize the breakingup of the gas bubbles. Although this device provides improved aerationefficiency, it suffers from the disadvantage that, when pumping liquidwaste which contains such materials as hair, the hair becomes entangledin the turbine blades, thus reducing the efficiency of the aerator.

Thus, the present invention provides an apparatus for mixing gases withliquids which may contain solid matters, e.g. hair, which will plug orfoul aeration devices known in the prior art.

SUMMARY OF THE INVENTION

In carrying out the principles of the present invention according to apreferred embodiment, an apparatus for mixing gas with liquids andpumping the resulting mixture comprises an outer cylindrical member, aninner cylindrical member, a base member, and a gas inlet member. Theouter and inner cylindrical members are arranged in a concentric manner,with one open end of each of the members being attached to the samesurface on the base member so that the ends of the cylindrical membersare completely sealed. The gas inlet member is disposed through theinner and outer cylindrical members and near the end attached to thebase member for the introduction of gas bubbles into the apparatus.Provided within the inner cylindrical member is at least one turbine,which is free to rotate along its longitudinal axis. Optionally,immediately upstream from each turbine, a venturi for restricting thecross-sectional area of the tube is provided. In addition, the openupper end of the inner tube may be provided with a check valve which maybe lifted by the buoyant force of the rising bubbles and which attains aclosed position when the gas applied to the apparatus is shut off. Theclosed check valve prevents the settlement of debris into the interiorof the inner cylindrical member. The apparatus is adapted for immersionvertically into the body of water to be aerated and/or pumped.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the apparatus of the present application;

FIG. 2 is the sectional view along line 2--2 in FIG. 1.

FIG. 3 illustrates the construction of a turbine used in this invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to an apparatus for introducing a gas (e.g. air)into a volume of liquid (e.g. water). The present apparatus may also beused as a pump for material transfer and for separating fineparticulates from a slurry.

As shown in FIG. 1, a preferred embodiment of the apparatus which isadapted for vertical immersion into the liquid to be aerated or pumped,comprises an outer cylindrical member 100 (second stage), an innercylindrical member 200 (first stage), a base member 300, and a gas inletmember 400. Outer cylindrical member 100 is mounted concentrically overinner cylindrical member 200, with the lower ends of the members beingmounted onto the same surface on base member 300 to form a seal. Gasinlet member 400 having one end open and the other closed is mounteddiametrically, transversely, and through concentric cylindrical members100 and 200, near the sealed lower ends thereof.

The outer cylinder member 100 comprises an elongated tube 101 having anopen upper end, 102, and a lower end, 103. A pair of diametricallyopposed, horizontal, ellipsoidal openings 104 are provided along thecircumference of tube 101. The distance between the opening and thelower end 103 of member 100 may be varied. However, the opening shouldnot be located above the top of the inner cylindrical member 200. On theother hand, the opening can be situated adjacent to base member 300. Thelocation of the openings depends on the amount of debris or solidspresent in the liquid to be pumped. In some particular applications, itmay be desirable to have the openings at a distance from the base, e.g.when there is a large amount of sedimentation present. The height of theopenings is from about 5% to 15% of the length of the tube, or up to thedifference in radius between the outer and inner members. As to thewidth of the opening, it may vary in accordance with the strength of thematerial used. As long as the outer member can support its own weight,the size of the opening can be so varied. Generally, it is between about30% to about 45% of the circumference of the tube.

The inner cylindrical member 200 comprises an elongated tube 201 havingan upper open end 202 and a lower end 203 (FIG. 2). The inside diameterof tube 201 is from about 1/4 to 2/3 of the inside diameter of tube 101.The height ratio of tube 101 to tube 201 is from about 4:1 to 1.25:1,preferably from about 2:1 to 1.5:1. Mounted on the interior surface 204of the tube is a plurality of venturis 205, 206. While only two venturisare shown in the drawings, any convenient number of venturis may beused, as required by the process. The venturis are for reducing thecross-sectional area of the tubing so that a higher liquid velocitytherethrough can be obtained. Mounted immediately downstream from eachof the venturis (i.e. the upper surface of the venturi) are turbines207, 208. These turbines are free to rotate about the longitudinal axisthereof and are caused to rotate solely by the buoyant force of therising gas bubbles. No external power source is connected to drive theturbines. The turbine has a diameter slightly less than the insidediameter of the venturi, to which it is mounted. The turbines aremounted at a distance apart and along the longitudinal axis of member201. They are preferably spaced at about one inner tube 201 diameterapart and a similar distance from each end of the tube. Although theturbines may be mounted on one common central shaft, the use of such ashaft is not essential. As shown in FIG. 3, turbine 301 may be mountedon a central shaft attached to hub 302 which is connected to venturi 303by means of a plurality of radially extending spokes 304. Thus, theturbines are so mounted that they are free to rotate about itslongitudinal axis. Turbines 207 and 208 are substantially identical insize in the preferred embodiment. The turbine or propeller blade designis such that the upward flow of liquid and air through tube 201 (andsolids entrained therein, if any) causes the turbines to rotate atrelatively high rates of speed. It is noted that the blades for adjacentturbines are set at different angles so that adjacent turbines rotate indifferent directions or at different speeds. For example, for turbine207, the blades are slanted from top left to lower right. Thus, turbine207 may rotate counter-clockwise, whereas turbine 208 rotates clockwise.The difference in rotational directions or speeds enhances the break-upof the rising bubbles. Although only two turbines are shown in FIG. 2,any number of turbines can be used, depending on the needs of theparticular process.

In the preferred embodiment, the upper end 202 of tube 201 is providedwith a freely moving check valve or cover 209. Check valve 209 may be inthe form of an inverted cone or a flat plate having an opening 210 atits center. The valve has a diameter which is slightly larger than theinside diameter of tube 201. Check valve 209 may be slidably-mountedthrough central opening 210 onto a vertical, central shaft 211 attachedto the hub of the uppermost turbine. Alternatively, check valve 209 maybe mounted on central shaft 211 attached to open end 202 by means of asuitable bracket (not shown). Check valve 209 is made of a materialwhich is sufficiently light weight so that it may be lifted solely bythe force of the rising bubbles. It is of utmost importance that checkvalve 209 be mounted in such a way that it can be easily opened by therising bubbles and closed when the gas supply to the apparatus is shutoff. In such a way, in the event that the apparatus has to be turnedoff, the check valve will cover open end 202 to prevent foreignmaterials from falling into and entangling the turbines, thus causingblockage and decreasing the efficiency of the apparatus. Check valve 209can be in any suitable configuration. For instance, it may be in theform of an inverted cone (as shown in FIG. 2) or a flat plate. In thecase of an inverted cone, the angle of inclusion, in FIG. 2 ranges fromabout 45° to about 70°. This angle may be varied according to the needsof the process in which the present apparatus is used. When theapparatus is used to pump and aerate only a liquid containing no solidor fibrous materials therein, there will be no problem with regard toplugging so that it is not necessary to include check valve 209 in thepresent apparatus.

Tube 201 is placed concentrically inside tube 101, as shown in FIGS. 1and 2. Lower ends 103 and 203 of cylindrical members 101 and 201 areattached to the same surface of base plate 300 to form a liquid-tightseal. It is of importance to note that ends 103 and 203 are completelysealed by base plate 300. This closed arrangement prevents the suckingof solid materials (e.g. hair) into the interior chamber of tube 201,thus eliminating problems with respect to plugging and entangling of theturbines. The material to be pumped enters tube 101 through openings 104and is lifted towards end 102, thus causing circulation. Base plate 300can be made of any suitable material provided that it is sufficientlyheavy and strong to stabilize the unit.

As shown in FIG. 2, gas inlet pipe 400 having open end 404 and closedend 403 is mounted diametrically and transversely through concentrictubes 101 and 201 and near the sealed lower ends of the tubes. Aplurality of openings 401 is provided in the middle portion of thetubing for introducing the gas into the interior chamber of tube 201.Optionally, openings 402 in tube 400 may be provided in the annularspace between tubes 101 and 201 to generate bubbles for additionalpumping energy (secondary pumping).

The apparatus as shown in FIG. 2 (i.e., in the concentric tubesarrangement) can be used for pumping solids-containing liquids, withoutany plugging problems. It should also be noted that when it is desiredto aerate a body of liquid, the present apparatus can be used withoutthe outer cylindrical member 100. In other words, for use as a materialtransfer pump, the apparatus comprises both inner and outer cylindricalmembers 100 and 200 (stages 1 and 2); for use as an aerator, theapparatus may comprise inner tube 201 only (stage 1) or both inner tube201 and outer tube 101 (stage 1 and 2).

It has been found that the present apparatus, when used as a pump doesnot give rise to any plugging problems, although a considerable amountof foreign solid materials, such as hair, may be present in the liquidto be pumped. The closed bottom ends construction of the concentrictubes prevents the foreign materials from entering into the inner tube.Thus, the possibility of the turbines being clogged or tangled iseliminated. Furthermore, the horizontal, ellipsoidal openings in theouter cylindrical member are sufficiently large to permit free passageof the foreign materials.

When in use, the apparatus is preferably completely submerged verticallyin the liquid to be aerated or pumped. For best efficiency, upper openend 102 of tube 101 should be at or below, mid-depth of the liquid inwhich the apparatus is immersed. In any event, for good efficiency,upper end 102 should be at least one outer tube 101 diameter below thesurface of the liquid. In the event that only the inner tube 201 isused, the upper open end 202 should be at, or below, mid-depth of theliquid to be circulated. Open end 202 should be at least one tube 201diameter below the liquid surface. Gas to be mixed with the liquid issupplied through inlet pipe 400 from a suitable source (not shown). Thegas leaves inlet pipe 400 through a plurality of orifices 401 to form amultitude of bubbles. As the gas enters the interior of tube 201, itrises toward the liquid surface in the form of bubbles. As the bubblesrise, they come into contact with the first turbine which is rotated bythe buoyant force of the bubbles. The rotation of the turbines causesthe bubbles to break up into a large number of small bubbles. The sizeof these bubbles is further reduced as they encounter the second turbinewhich is rotating in a direction opposite to or at a different speedfrom that of the first turbine. As a result, a large number of verysmall bubbles leaves the open end of tube 101. These small bubblesprovide a large surface area for mass transfer, thus increasing theefficiency of the gas-liquid mixing process.

Typical dimensions for inner tube 201 are 4 inches in diameter and 8inches in height, and for outer tube 101, 8 inches in diameter and 15inches in height. Inner tube 201 may also be 8 inches in diameter, 16inches in height, and for outer tube 101, 12 inches in diameter and 30inches in height. The dimensions of the tubes can, of course, be changedin accordance with the magnitude of the process to which the apparatusis applied.

As to the flow rate of gas or air to be applied through the apparatus,it may be varied according to the needs of the particular process.Preferably, for an apparatus having a 8-inch diameter inner tube and a12-inch diameter outer tube, a gas flow rate of from about 10 to about20 SCFM is used. For an apparatus having a 4-inch diameter inner tubeand an 8-inch diameter outer tube, a gas flow rate of from about 3 toabout 5 SCFM is preferred.

The present apparatus finds application in a variety of processes. Forexample, the present apparatus comprising both outer and inner tubes maybe used for aerating sludge or sewage, without any clogging or pluggingproblems.

As another application, the present apparatus having both inner andouter tubes may be used in the separation of olives in the foodindustry. In making the separation, it is desired to separate thoseolives having a smooth surface from those with jagged surfaces, whichare undesirable. The olives are deposited in a tank which is filled withwater at a height sufficient for the present apparatus to be operative.Air is introduced into the present apparatus, which comprises both innerand outer tubes, to generate circulation in the olive and water mixture.Those olives which have a jagged surface are pumped to the top of thetank. A possible explanation of this phenomenon is that air bubbles maybe lodged in the jagged surface, thus causing the unacceptable olives tofloat. The undesirable olives may then be removed by skimming. Theacceptable olives, i.e., those with a smooth surface, remain in thebottom of the tank. Thus, a separation of unacceptable and acceptableolives can be achieved by using the present apparatus.

It has further been found that the present apparatus may be used toseparate fine particles from a slurry containing solid fine particles.In this instance, a one stage (i.e. inner tube only) or a two stage(both inner and outer tubes) apparatus may be used. The slurry to beseparated is deposited in a suitable container in which the presentapparatus is immersed. The height of the slurry is maintained at a levelin which the present apparatus is operative. Compressed air (or anyother useful gas) may then be introduced into the apparatus to generatebubbles. The fine particles contained in the slurry are pumped out ofthe apparatus, thus leaving a clear liquid within the lower portion ofthe interior of tube 201. This clear liquid may then be removed from theinterior of tube 201. The particulates generally have a diameter rangingfrom about 5 to about 100 microns and are formed of a material heavierthan water. Thus, there is provided a method for removing fine particlescontained in a slurry. To cite a practical example, the presentapparatus, either in the one stage or two stage mode, may be used forseparating coal particles from a slurry comprising water and such coalparticles.

The materials used in the construction of the apparatus of the presentinvention may be any noncorroding material (depending upon the liquid inwhich the apparatus is to be used). Tubes 101 and 201 may be stainlesssteel, polyvinyl chloride plastic, or fiberglass. The turbines may bestainless steel or urethane plastic. The shaft 211 may be stainlesssteel.

The foregoing description has been by way of illustration example only,and no limitation is thereby intended, the scope of the invention beinglimited solely by the claims.

What is claimed is:
 1. A process of aerating a body of liquidcomprising:placing vertically in said liquid an apparatus for mixing gaswith liquid, said apparatus comprising:(a) an inner cylindrical membercomprising an elongated tube having upper and lower ends and a pluralityof turbines, which are free to rotate about the longitudinal axisthereof mounted within the tube, the turbines being spaced apart fromone another and so constructed that adjacent turbines have differentrotational direction or velocity, the tube having a solid, imperforatewall; (b) an outer cylindrical member comprising an elongated tubehaving upper and lower ends and a plurality of openings in the lowerhalf of the tube wall, the outer and inner cylindrical members beingarranged in a concentric manner; (c) a base member, to one surface ofwhich the lower ends of the inner and outer cylindrical members areattached so that the lower ends are completely sealed; and (d) a gasinlet pipe for introducing gas bubbles into the lower end of at leastone of the cylindrical members; and supplying a sufficient amount of airto said gas inlet pipe to cause aeration and pumping of the liquid. 2.The process of claim 1 wherein the liquid is sludge.
 3. A process ofseparating particles having a smooth surface from particles having ajagged surface comprising:immersing vertically in a mixture of saidparticles and water an apparatus comprising;(a) an inner cylindricalmember comprising an elongated tube having upper and lower ends and aplurality of turbines, which are free to rotate about the longitudinalaxis thereof mounted within the tube, the turbines being spaced apartfrom one another and so constructed that adjacent turbines havedifferent rotational direction or velocity, the tube having a solid,imperforate wall; (b) an outer cylindrical member comprising anelongated tube having upper and lower ends and a plurality of openingsin the lower half of the tube wall, the outer and inner cylindricalmembers being arranged in a concentric manner; (c) a base member, to onesurface of which the lower ends of the inner and outer cylindricalmembers are attached so that the lower ends are completely sealed; and(d) a gas inlet pipe for introducing gas bubbles into the lower end ofat least one of the cylindrical members; circulating the mixture throughsaid outer cylindrical member in said apparatus; and skimming off theparticles with the jagged surface which collect near the air-waterinterface.
 4. A process of separating a clear liquid from a slurrycomprising the liquid and fine solid particles comprising immersingvertically in said slurry an apparatus comprising:(a) an innercylindrical member comprising an elongated tube having upper and lowerends and a plurality of turbines, which are free to rotate about thelongitudinal axis thereof mounted within the tube, the turbines beingspaced apart from one another and so constructed that adjacent turbineshave different rotational direction or velocity, the tube having a solidimperforate wall; (b) an outer cylindrical member comprising anelongated tube having upper and lower ends and a plurality of openingsin the lower half of the tube wall, the outer and inner cylindricalmembers being arranged in a concentric manner; (c) a base member, to onesurface of which the lower ends of the inner and outer cylindricalmembers are attached so that the lower ends are completely sealed; and(d) a gas inlet pipe for introducing gas bubbles into the lower end ofat least one of the cylindrical members; circulating the slurry throughsaid outer cylindrical member in said apparatus; and removing the clearliquid collected within said inner cylindrical member and at the bottomthereof.
 5. The process of claims 1, 3 or 4 wherein in the innercylindrical member, immediately upstream from each turbine, a venturi isprovided to increase the velocity of the liquid flowing therethrough. 6.The process of claims 1, 3 or 4 wherein the ratio of the diameters ofthe outer and inner tubes is from about 4:1 to about 1.5:1 and the ratioof the heights of the outer and inner tubes is from about 4:1 to about1.25:1.
 7. The process of claims 1, 3 or 4 wherein the top end of theinner cylindrical member is provided with a check valve which is openedby the buoyant force of the rising bubbles and closed when gas supply tothe apparatus is shut off to prevent the settlement of solid mattersinto the interior of the inner cylindrical member.
 8. The process ofclaims 1, 3 or 4 wherein the gas is introduced into the interior of theinner cylindrical member.